Abstract Clay minerals in soils contain ubiquitously abundant interlayer spaces; however, the vital role the interlayer plays in determining the adsorption and stability of aqueous species is still enigmatic. The aim of this work is to systematically address the specific elevated adsorption characteristics and underlying mechanism in the clay interlayer by carefully comparing with those at the external surface. A series of cations (Na+, K+, Cs+, Ca2+, Pb2+, Cd2+, Ba2+, and Zn2+) are considered and the molecular dynamics methods are conducted. The interlayer of clay minerals is highly compacted, and the electric double layer (EDL) structures of neighboring surfaces extensively overlap. This results in specific elevated adsorption and stability of cations confined in the interlayer, as compared to the external surface. The adsorption modes remained the same whereas the interfacial distributions clearly changed, and the adsorption numbers increased. The local structure alteration was obviously more pronounced for divalent (M2+) rather than monovalent (M+) cations, and M2+ ions were coordinated stably to approximately six surface oxygens on each side of the interlayer surface. Extremely condensed time-evolution trajectories of the interlayer cations predicted an enhanced stability, which was further evidenced by the generally increased averaged residence time with surface oxygens and substantially reduced diffusion coefficients. These results address the vital role of the clay interlayer in determining the adsorption and retention of metal ions in a soil solution, which may further help to manage radioactive and heavy metal ion pollution.

中文翻译：

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与粘土矿物外表面相比，夹层中阳离子的特定吸附和稳定性提高

摘要 土壤中的粘土矿物普遍存在丰富的层间空间；然而，夹层在决定水性物质的吸附和稳定性方面所起的重要作用仍然是个谜。这项工作的目的是通过与外表面的那些进行仔细比较，系统地解决粘土夹层中特定的吸附特性和潜在机制。考虑了一系列阳离子（Na+、K+、Cs+、Ca2+、Pb2+、Cd2+、Ba2+ 和 Zn2+）并进行了分子动力学方法。粘土矿物的夹层高度压实，相邻表面的双电层 (EDL) 结构广泛重叠。与外表面相比，这导致限制在夹层中的阳离子的特定提高的吸附和稳定性。吸附模式保持不变，而界面分布明显改变，吸附数增加。二价（M2+）而不是单价（M+）阳离子的局部结构改变明显更明显，并且M2+离子稳定地与夹层表面每一侧的大约六个表面氧配位。层间阳离子的极度浓缩的时间演化轨迹预测了稳定性的增强，这进一步通过表面氧的平均停留时间普遍增加和扩散系数显着降低来进一步证明。这些结果解决了粘土夹层在确定土壤溶液中金属离子的吸附和保留方面的重要作用，这可能进一步有助于管理放射性和重金属离子污染。